Referring to FIG. 1, an illuminating device 1, such as a vehicle lamp, is shown to include a lamp cover 11, a flexible printed circuit board 12, a plurality of light-emitting diodes 13 disposed on the flexible printed circuit board 12, and a substrate 14. The lamp cover 11 has a plurality of cover bodies 111 each of which is formed with a through hole 112. The substrate 14 has a main body 141 for supporting the flexible printed circuit board 12, and pairs of heat rivets 142 protruding from one side of the main body 141 to interconnect the lamp cover 11 and the substrate 14.
When assembling the aforesaid illuminating device, the light-emitting diodes 13 are first disposed onto the flexible printed circuit board 12, followed by bending the flexible printed circuit board 12 into a wave-like structure, including a plurality of spaced-apart arc portions 121 and a plurality of flat portions 122 alternately arranged with the arc portions 121. Thereafter, the flat portions 122 are then disposed onto the main body 141 of the substrate 14, such that the heat rivets 142 extend respectively through engaging holes 123 which are formed in the flat portions 122. Then, the lamp cover 11 is disposed onto the soft printed circuit board 12, such that each of the light-emitting diodes 13 is received in the through hole 122 of a respective one of the cover bodies 111 and that each of the arc portions 121 is disposed between two adjacent cover bodies 111. Finally, the heat rivets 142 are hot-melted to interconnect the substrate 14 and the lamp cover 11. However, since the heat rivets 142 need to be hot-melted to interconnect the substrate 14 and the lamp cover 11, and since the illuminating device 1 has a relatively large amount of components, labor cost as well as the assembling time may be increased, resulting in relatively high production costs.